Most motor vehicles utilize some type of cable system to engage and release the rear brakes to act as a parking brake. The parking brake system basically includes a pedal or lever actuator, a front cable strand, a left rear cable strand, a right rear cable strand, a front cable conduit, a left rear cable conduit, and a right rear cable conduit through which the front and rear cable strands extend, respectively, an equalizer assembly positioned between the front and rear cable strands, tensioning rod and nut, cable connector and left and right rear brake assemblies. The left and right rear cable strands are attached to the left and right rear brake assemblies, respectively.
The following is a description of the general operation of a park brake system to assist in understanding the invention. A brake pedal or lever is actuated to apply tension to the front cable strand. The front cable strand is connected to the left and right rear cable strands through an equalizer. The function of the equalizer is to equally distribute tension in the front cable to the right and left rear cables so that the tension is balanced between the cables extending to the left and right rear brake assemblies when the lever is actuated. The added tension applied to the rear cable strands overcome the spring in each rear brake assembly to cause the brakes to engage and act as a parking brake. The spring normally holds the rear brake shoes or calipers open and thus disengaged.
In operation, it is desirable that high tension exists in the cables even when the pedal or lever is in the non-actuated position (residual tension). Adequate residual tension in the cable system means that the pedal or lever does not have to be extended a great distance to achieve a strong force at the brake assemblies to provide for secure engagement. Furthermore, the high tension helps eliminate the slack and voids in the cables and conduits, which reduces creep or lengthening of the cable thus making consistent the range of motion of the lever. This same high level of consistency in actuator travel will also exist from vehicle to vehicle.
The objective at the time of installation of the park brake cable system is, therefore, to introduce enough high tension to the cables so that "voids" in the conduit system and cable stretch are effectively removed. In this way the system will not continue to loosen-up over repeated actuation and there will be continued consistency in pedal or lever travel over the life of the vehicle and from vehicle to vehicle. This objective is difficult to achieve in a rapid and inexpensive manner such as required in a high volume automotive assembly line environment.
Various methods of tensioning the cable system are used, all with the goal of introducing enough tension to the cable system during installation to remove voids minimize variation in actuator travel from vehicle to vehicle. One method of tensioning the cable system is to tension the cables during installation to a level where the brakes are almost starting to drag and no further. In this method a predefined level of tension is determined and the park brake cable system of all the vehicles on the assembly line are tensioned to this level. This method typically results in wide variation in lever travel from vehicle to vehicle and also results in a system that loosens-up over time since the voids in the cable and conduit are not sufficiently removed. Merely tensioning to a level just below brake drag does not introduce enough initial tension to completely remove system voids and eliminate cable stretch.
Another method is to tension the cable system during installation to a level far beyond what is required to merely engage the brakes. In doing so, many of the voids in the cable and conduit system are removed and the cable stretch accomplished. The tension in the cable system is then reduced just enough until the brake assemblies are no longer engaged. This method results in an optimally tensioned park brake cable system, however, it is time consuming because the cables must be initially tensioned to a very high level and then de-tensioned to a desired residual tension level. Expensive instruments are required to measure the tension in the cable system at both the tensioning and de-tensioning steps to insure the final or residual tension in the cable system is adequate. This method takes a relatively long time to perform during production of the vehicle.
There is a continuing need in the art for an improved park brake cable system and method for adjusting, including a cable connector clip, that provides the proper amount of tensioning and tension relief for consistent park brake performance for a vehicle, and minimal variation of park brake performance from vehicle to vehicle. It is with the shortcomings of the prior art in mind that the instant invention was developed.